3. A syringe filled with air can be used to test the relationship between the te

ID: 789834 • Letter: 3

Question

3. A syringe filled with air can be used to test the relationship between the temperature and the volume of a

sample of gas. The syringe has a movable plunger that allows an enclosed sample of gas to be held at a

constant external pressure, so the gas inside the syringe can be held at a constant total pressure of 1.00 atm

while allowing the volume of the gas to increase or decrease.

a) You fill a syringe with 5.0 mL of air at 25C and 1.00 atm. How many moles of air are contained in the

syringe?

b) Assuming that the mole fraction of nitrogen in air is 0.79 and the mole fraction of oxygen in air is 0.21,

determine the partial pressure of each gas, and the mass of each gas contained in the syringe.

c) On repeating the experiment, you accidentally trap a small amount of water inside the syringe. (Assume

that the water vapor reaches equilibrium inside the syringe, and neglect the volume of the liquid water

which will be present.) Given a temperature of 25C, a volume of 5.0 mL, and a total pressure of 1.00

atm, determine the partial pressure of water vapor and the partial pressure of air (without water vapor)

inside the syringe.

d) You increase the temperature of the syringe to 65C; the total pressure remains 1.00 atm, but the volume

increases. Determine the volume of the syringe at the new temperature. (Assume that the water vapor

reaches equilibrium at 65C.)

a) at STP 1 mole of gas occupies 22.4L volume = 22400 mL

so,

22400 mL -----------------> 1 mole

5mL ------------------------>?

=5/22400 = 0.00022 moles

b) Pi = Xi * P

where, Pi is partial pressure, Xi is mole fraction, P is total pressure

Partial pressure of nitrogen = 0.79 * 1 = 0.79 atm

Partial pressure of oxygen = 0.21 * 1 = 0.21 atm

d) P1V1/T1 = P2V2/T2

given that, P1= 1 atm, V1 = 5 mL, T1 = 25

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